This project will be directed at the characterization, in vitro, of the relationship between the physiologic effect of angiotensin II (A-II) and its binding to proposed receptor molecules. Isolated adrenal glomerulosa cells and the aorta will serve as model systems. Saturable binding of A-II and either aldosterone production by glomerulosa cells or contraction of aortic strips will be measured under identical experimental conditions in the same pool of tissue. These parameters will be measured with respect to time and with respect to drugs which have been reported to increase or decrease saturable A-II binding. The hypotheses that A-II receptors in various tissues are different and that receptor properties may be altered by various experimental conditions will be tested. Toward this end several binding properties of the receptor will be measured. These are: K, the apparent equilibrium association constant for A-II; n, the number of binding sites; and pA2, the apparent dissociation constant of competitive antagonist of angiotensin. These binding properties will be estimated in tissues of animals subjected to experimental conditions reported to alter the responsiveness of target organs to A-II or various types of hypertension.